Linux Decides To Disable RNG On All AMD fTPMs

As a follow-up to the first-on-Phoronix article last month that highlighted Linus Torvalds' frustrated views on the AMD fTPM random number generator continuing to cause problems for users even with updated firmware/BIOS, as of today the Linux kernel has gone ahead and blanket disabled RNG use for all current AMD fTPMs.

AMD Linux engineer Mario Limonciello authored the patch that was merged today to disable the RNG for all AMD fTPMs. Mario summed up in that commit:

tpm: Disable RNG for all AMD fTPMs

The TPM RNG functionality is not necessary for entropy when the CPU already supports the RDRAND instruction. The TPM RNG functionality was previously disabled on a subset of AMD fTPM series, but reports continue to show problems on some systems causing stutter root caused to TPM RNG functionality.

Expand disabling TPM RNG use for all AMD fTPMs whether they have versions that claim to have fixed or not.

This patch was merged to mainline today for the Linux 6.5 kernel while the patch is also marked for back-porting to the Linux 6.1 and newer stable kernels where this AMD fTPM RNG use is present. Thus over the next few days this change in behavior for modern AMD Ryzen systems will be rolling out in the next set of stable kernel point releases.

Hopefully this will lay to rest the various AMD stutter issues that continue to be reported by Linux users on recent kernel versions.